An apparatus for measuring objects is used to determine geometrical parameters of workpieces. In particular sensing balls can be provided as measuring tips. It is possible to distinguish between switching systems and measuring systems with the probes of conventional coordinate measuring units. In the switching systems, an electrical contact is opened or closed in the probe by a sampling of the object surface by the sampling body and the contact is thereby detected. Switching systems can be manufactured simply and inexpensively. However, a point can only be sampled once in one direction. For a further sampling, the electrical contact has to be set into its original state again, that is the sampling body has to be returned to its original position again, whereby a time delay occurs. The measuring systems have a separate 3D measuring system in the probe by which the position of the measuring tip relative to the probe can be determined. Capacitive sensors or strain gages can in particular be provided. The measuring tip can thus continuously remain in contact with the object to be measured during the measuring procedure. A continuous measurement is thereby possible. Coordinate measuring units with a measuring probe are therefore in particular suitable for scanning applications.
Probes for object measurement apparatus of the described kind are usually designed for a sampling force of 0.08 N to 1 N. Measurements with particularly small sensing balls—e.g. with sensing balls of less than 0.5 mm diameter—and with particularly thin sampling bodies—e.g. with sampling bodies which are thinner than 0.3 mm—are thereby made difficult. An undesirably poor repetition precision can in particular result in the measurement by a bending of the sampling body used.